The present invention relates to a semiconductor device functioning as a bistable memory or a logic circuit and including a MIS semiconductor element, a hot electron transistor, a resonance tunnel diode, that is, a non-linear element, and the like formed on a common substrate, and also to a method of manufacturing the semiconductor device.
Recently, various types of elements whose operational principle is totally different from that of a MIS semiconductor element have been proposed, and a resonance tunnel element is one of these recently proposed elements. A resonance tunnel element has a "double barrier structure", in which a semiconductor thin film, having a thickness sufficiently small to cause a quantum effect, is sandwiched between energy barrier films of an oxide film or the like and electrodes are formed on the outer faces of the energy barrier films. The electric characteristic of the resonance tunnel element is controlled by a resonance tunnel effect that application of a given voltage between the two electrodes simultaneously causes tunneling of electrons between the semiconductor thin film and the two electrodes. Many of conventional resonance tunnel diodes are obtained by using a compound semiconductor (Tsu, Esaki et al., Appl. Phys. Lett., 22, 562 (1973), etc.). This is because the compound semiconductor has the following advantages: The compound semiconductor is a direct transition type semiconductor material and has a small effective mass, in which the resonance tunnel effect can be easily caused; the compound semiconductor can be used as an energy barrier film because of its semi-insulating property; and the compound semiconductor can be easily formed into a thin film by utilizing the epitaxial growth because it is a crystalline material.
In contrast, there is a demand for a resonance tunnel element made from a general semiconductor material such as silicon because the compound semiconductor has limited application in view of the manufacturing cost. However, silicon is an indirect transition type semiconductor material, and its effective mass is larger, namely, the mobility is smaller, than that of the compound semiconductor and hence, the resonance tunnel effect cannot be easily caused. In addition, when silicon is used, a silicon oxide film, a silicon nitride film or the like is used as the energy barrier film, but the silicon oxide film or the like is an amorphous material and hence is very difficult to be formed by the epitaxial growth.
On the other hand, another example of the elements utilizing the quantum effect apart from the resonance tunnel element includes a hot electron transistor. The hot electron transistor has the "double barrier structure", in which a semiconductor thin film, having a thickness sufficiently small to cause the quantum effect, is sandwiched between energy barrier films of an oxide film or the like and electrodes are formed on the outer faces of the energy barrier films. In this structure, when a voltage is applied between one electrode and the semiconductor film, hot electrons tunnel through one energy barrier film to be injected into the semiconductor film from the electrode. The injected electrons lose their energy within the semiconductor thin film owing to the lattice vibration or the like, but when the semiconductor film is thin, a certain proportion of the electrons can pass through the semiconductor film. Since another energy barrier film is formed in contact with the semiconductor film, hot electrons alone can reach another electrode through this energy barrier film. Electric power can be amplified by making a current flowing from one electrode through the semiconductor film to the other electrode be larger than a current flowing from one electrode into the semiconductor thin film by providing any structural means. Such an element can be advantageously operated normally even at a low temperature because it does not include a pn junction as a bipolar element. Many of conventional hot electron transistors are realized by using a compound semiconductor. This is because the compound semiconductor can be used as an energy barrier film because of its semi-insulating property and can be easily formed into a very thin semiconductor film by the epitaxial growth since it is a crystalline material.
Although the resonance tunnel diode is an element with a large number of possibilities, it is difficult to constitute a variety of circuits by using the tunnel diode alone because it has merely two terminals, i.e., two electrodes.
Furthermore, with regard to the hot electron transistor, the usage of the compound semiconductor limits its application in view of the manufacturing cost, and there is a demand for a hot electron transistor made from a general semiconductor material such as silicon. However, since silicon is not a semi-insulating semiconductor material, a silicon oxide film, a silicon nitride film or the like is used as an energy barrier film. Therefore, in order to sandwich a semiconductor thin film with two energy barrier films, it is necessary to form a monocrystalline silicon film on the silicon oxide film or the like. However, it is very difficult to epitaxially grow the monocrystalline silicon film on the silicon oxide film or the like, that is, a film of an amorphous material, because lattice mismatching is caused in such a case.